Joint for endless belts

ABSTRACT

A film-casting belt is composed of flexible metal of high hardness, especially stainless steel but possibly ordinary steel, copper and nickel, and has a thickness up to about 1 mm. The belt joint is made by butt-welding the ends of the band and a bias such that the weld seam runs at an angle to the direction of movement to the belt which ranges between 2* and 45* but preferably is between 2* and 15*. The weld seam is ground flush with the surface of the belt which has a tolerance + OR - 3 Mu . The curvature of the band, which is maintained under tensions up to 200 tons, may be reversed to facilitate stripping of the synthetic-resin or cellulosic film from the surface.

United States Patent 1191 Stadler et al.

[ JOINT FOR ENDLESS BELTS [75] Inventors: Hubert Stadler, Berndorf;Horst Spanyar, Braunau am Inn, both of Austria [73] Assignee: VereinigteMetallwerke Ranshofen- Berndori Aktiengesellschaft,Braunau-amlnn-Ranshofen, Austria [22] Filed: Nov. 30, 1970 [21] Appl.No.: 93,538

Related US. Application Data [63] Continuation-impart of Ser. No.693,889, Dec 27,

1967, abandoned.

[56] References Cited UNITED STATES PATENTS 862,558 7/1907 Hiscock..425/47l X 1451 Apr. 17, 19:73

Primary ExaminerH. A. Kilby, Jr. Att0mey-Karl F. Ross I 5 7 ABSTRACT Afilm-casting belt is composed of flexible metal of high hardness,especially stainless steel but possibly ordinary steel, copper andnickel, and has a thickness up to about 1 mm. The belt joint is made bybuttwelding the ends of the band and a bias such that the weld seam runsat an angle to the direction of movement to the belt which rangesbetween 2 and 45 but preferably is between 2 and 15. The weld seam isground flush with the surface of the belt which has a tolerance i 3 u.The curvature of the band, which is maintained under tensions up to 200tons, may be reversed to facilitate stripping of the synthetic-resin orcellulosic film from the surface.

6 Claims, 8 Drawing Figures PAIENIEBAPRH 3.728.066

SHEET 1 BF 2 SUEFACE GROUND PLANAR r0 2 a- 3 1 Huber? Sfadler HorsfSpanyar I N VEN TORS BY R o W Attorney PATENTEDAPR 1 H973 SHEET 2 [IF 2Huber? Sfadler Horsf Span ar. INVENTORg Y Attorney m GI V/Atik w JOINTFOR ENDLESS BELTS CROSS REFERENCE TO COPENDING APPLICATION Thisapplication is a continuation-in-part of our application Ser. No.693,889 filed 27 Dec. 1967 now abandoned and entitled JOINT FOR ENDLESSBELTS".

FIELD OF THE INVENTION seam for the casting of films; the invention alsorelates to ajoint for such belts.

BACKGROUND OF THE INVENTION In the formation of synthetic-resin orcellulosic films, it is common practice to spray or doctor thefilm-forming material onto a continually endless surface which carriesthe congealing film through a heating zone at which the solvent isdispelled and then into a stripping zone at which the film is removedfrom the surface.

Such belts are frequently constituted of metal and must have a hard,highly finished surface of limited dimensional tolerance. Since the beltmust pass over rollers, it must be highly flexible and because anydeformation of the belt will result in a corresponding defect in thefilm, the belt must be rigid during the casting and drying steps. Suchrigidity is obtained by the application of high tension forces to thebelt.

For the most part, such belts are formed by joining the ends of the beltin a carefully prepared lap weld running perpendicularly to thedirection of movement of the belt. This has the disadvantage that theseam is a weak point and, indeed, prior'art belts tend to rupture atthis seam. The problem is increased by the fact that, where the seamcontacts the rollers, it is bent therealong and lies along a generatrixof the roller and is subjected to severe bending stress. When the bandleaves the roller, it straightens, thereby bending the band at the weldseam in the opposite direction. Furthermore it may be desirable toreverse the curvature of the band to facilitate stripping as describedbelow, whereupon an additional stress is provided. Hence the elevatedtensile stress applied to the band to maintain its stiffness and thequality of its surface, the repeated bending stresses generated at theweld seam and the resulting material fatigue, cause failure of the belt,especially at the seam.

A further disadvantage, brought out in the aforedescribed copendingapplication, is the fact that, when the seam lies perpendicular to thedirection of movement of the belt, the entire seam passes at oncebeneath the pouring apparatus from which the filmforming material isdispensed. If a cavity is formed at the seam, e.g., by the grinding ofthe scam flush with the belt surface or by the tensile stresses appliedat the scam, the gap between the receiving surface of the belt and thepouring apparatus will increase and the thickness of the film altered.This is, of course, a consequence of the fact that the entire seam isdisposed beneath the pouring apparatus and lies along a generatrix ofthe support roller at once.

OBJECT OF THE INVENTION It is the principal object of the presentinvention to provide a metal-foil belt for the casting of syntheticresinand cellulosic film in which the aforementioned disadvantages areobviated.

Another object of the invention is to provide an improved jointstructure for such belts.

It is also an object of our invention to provide a dimensionally stablebelt for the casting of film which will yield a film of higher qualityand will suffer less frequently from breakdown than theretofore.

SUMMARY OF THE INVENTION We have now discovered, most surprisingly, thatthe aforementioned disadvantages can be eliminated and the listedobjects gained by providing a film-casting belt which consists of metal,especially stainless steel, but possibly also ordinary steel, nickel orcopper, having a seam extending generally oblique to the direction ofmovement of the belt, the seam being formed as a butt weld rather thanas the lap-type weld current heretofore.

The important feature of the invention is that the metallic band has athickness up to about 1 mm and that the butt-weld seam runs athwart thebelt at an angle between 2 and 45 to the direction of movement of thebelt. The angle of inclination of the seam is preferably 2 to 15 (to thelongitudinal edge). The fact that the seam intersects the guide rollersto an angle to its generatrices insures that the stress applies only tolimited regions of the seam at any time, whereby unstressed portions ofthe seam serve to support the stressed portions of the seam againstbreakage. Moreover, since only a limited portion of the seam is locatedin the pouring gap at any given moment, there is no sharp alteration inthe gap width simultaneously across the entire length of the pouring gapand hence no material change in the thickness of the film which isobtained.

In the aforementioned copending application, we have pointed out thatthe prior-art drawbacks are avoided by providing connecting seamsoblique with respect to the side edges. Such an arrangement enables onlypartial passage of the welding seam over the guide roller at a givenmoment so that only that part of the seam is subjected to extraordinarystress. Unevenness in the welding seam cannot have too disadvantageousan effect in this arrangement.

According to a more specific feature of the invention, the oblique weldseam may extend continuously across the entire transverse width of thebelt. Alternatively, the belt may be built up of a plurality oflaterally juxtaposed belt sections which are joined by a longitudinalseam, i.e. a seam extending in the direction of movement of the beltwhile the oblique seams of each section include angles of 10 to 45 withthe longitudinal seam. In this embodiment, the oblique seams of theplurality belt sections preferably are aligned with one another, i.e.form a single continuous oblique seam. According to another embodimentof the invention, the belt is formed by winding a single band generallyhelically so that a correspondingly formed seam is produced, the seamhaving a pitch angle between about 2 and 8.

In all cases, means may be provided for tensioning the band to about 200tons and/or for inverting the curvature of the band to facilitatestripping of the film from the surface of the band. Since the obliquejoint of the present invention has its specific importance infilm-casting conveyors, the apparatus of the present invention isunderstood to include means for casting the film-forming material upon asurface of the belt and forming, therefore, a pouring gap therewith,means for vaporizing the solvent, and means for stripping the film fromthe belt upon vaporization of the solvent.

DESCRIPTION OF THE. DRAWING readily apparent from the followingdescription,'

reference being made to the accompanying drawing in which:

FIG. 1 is a diagrammatic perspective view showing a film-casting beltaccording to the present invention, made up of two belt sections inlateral juxtaposition;

FIG. 2 is a similar view of a belt formed by helical winding of asuitably shaped metal band;

FIG. 3 is a perspective view, also in diagrammatic form, of an apparatusfor the casting of synthetic resin film;

FIG. 4 is a cross-sectional view taken along the line IV IV ofFlG. 3;

FIG. 5 is an end view illustrating the inversion of the curvature of theband for stripping the film thereof;

FIGS. 6 and 7 are views similar to FIG. 1 illustrating otherarrangements of the oblique seam; and

FIG. 8 is an elevational view showing the utilization of the band ofFIG. 2 in a film-forming apparatus.

SPECIFIC DESCRIPTION In FIG. 1, we have shown a metal film-castingconveyor of double breadth made up of two strips of normal breadth whichhave been welded together laterally along their longitudinal edges inthe direction of movement of the conveyor via the weld seam 3. The outeredges 7 thus constitute the longitudinal edges of the double-breadthbelt produced from the two sections 1 and 2 and lie in planesperpendicular to the casting surface. The sections 1 and 2 areindividually joined into endless bands by oblique seams 4 which includean angle a in the direction of advance of the belt (arrow A) rangingbetween 10 and 45 and preferably between 10 and In this embodiment, theoblique weld seams 4 are aligned with one another and are buttwelds asdescribed below in connection with FIG. 4.

In the embodiment of FIG. 2, the oblique seam has been lengthened bydecreasing the angle so that, for example, the angle ranges between 2and 8. In this case, a central seam can be eliminated and the obliqueseam formed as a helix. The band between the longitudinal edges 7 has awidth greater than the width of the band from which it is formed. Whileonly somewhat more than a single complete turn of the helix is providedin this embodiment, the band may be made up of any number of such turnsor turn fractions. The result is a screw-type joint which practicallyfunctions as a longitudinal seam but serves as well to join the band inan endless configuration (see FIG. 8).

As represented in FIG. 3, onlya single band section l0,need be providedand its oblique seam 11 may include an angle 7 of, say, 10 with thelongitudinal edges 12 and 13 of the band. The total length L of theoblique seam may be less than the length of the longitudinal edge 7. Lis greater than the length of the longitudinal edge 7' in FIG. 2. L inFIG. 3 is shown to be greater than the circumference C of the guiderollers 14 and 15 over which the belt passes. The guide rollers have adiameter D so that the circumference C 1rD. In FIG. 3, moreover, we showa casting nozzle 16 from which a band of film-forming synthetic resin orcellulosic material is deposited at 17 upon the surface 18 of the belt10 for vaporization of a solvent by heating in the subsequent stretch.The heating means is represented at 19in FIG. 3.

Beyond the heating means, a stripper 20 removes the finished film 21,preferably at a point of direction change of the belt 10 to facilitatesuch removal. Arrow 22 represents the tension applied to the belt whichmay be of 200 tons, for example. The weld seam 1 l is shown in crosssection in FIG. 4 from which it can be observed that the seam is a buttweld with beads of weldment 23 introduced between the edges of the beltand ground flush with the surface 18 thereof so that the surfacetolerance is :3 The thickness of the metal belt is ap proximately 1mmand the belt is preferably composed of stainless steel. Advantageously,prior to grinding, the weld is compacted by cold or hot rolling orhammering, thereby densifying the weldment. In fact, when the surface ishammered or rolled smooth, grinding may be omitted. In addition, we mustpoint out that the term welding as used herein is intended to includesoldering in which the bead is formed by low-melting solder;

In FIG. 8, we show the use of the band of FIG. 2 in a film-formingapparatus in which it is assumed that the film has initially beenproduced elsewhere and is fed at 30 to the belt 6 whose helical seam 5has a pitch angle [3 of 2 to 8 as previously noted. The film 30 is fedat this pitch angle and in the same pitch sense as shown in FIG. 8 sothat, whenever the helical seam meets the band, it will coincide withthe junction between turns of the helical strip, the latter being fedfrom the apparatus at 31. While the film is drying on the heated metalbelt,

it may be trimmed by blades 32 and 33 at the Iongitudinal edges 7' ofthe belt.

In FIG. 5, we have shown an arrangement in which a heated drum 40 orguide roller is subtended by an endless metal belt 41 which has ahelical seam over a length greater than the arc length of the band incontact with the heated drum or roller 40, the latter being at atemperature of 200C. The belt passes about idler and drive rollers 42,43, 44 and 45, the rollers 43 and 44 being tensioned at T to apply atensile stress of 200 tons to the belt. At the roller 45, the film iscast onto the belt 41 via a nozzle arrangement 46, the film 47 moving onthe belt to contact the roller 40 for drive thereon. A pressure roller48 may serve to calibrate the thickness of the film. The film isstripped at 49 upon its emergence from the gap between the belt and theroller 40 and as the belt 41 is deflected about the roller 42 to invertits curvature.

FIGS. 6 and 7, show that the seams 4' of the two-sec tion belt 1', 2',joined by the longitudinal seam 3', can

be parallel to one another but staggered in the direction of movement ofthe belt. In the modification of FIG. 7, the oblique seams 4" convergetoward one another in the direction of belt movement (arrow B) andterminate at a common vortex of longitudinal seam 3" of the sections 1"and 2". In the systems of FIGS. 5-8, of course, the seam has the sameconstruction as already described for FIG. 4.

We claim:

1. A belt or the formation of a film strip from a filmforming material,comprising a metal-foil band having complementary edges 'joined togetherin a butt seam with metal bonding flush with the surfaces of the belt,said band being of generally flat configuration with longitudinal edgeslying in planes perpendicular to the band surface, said seam extendingathwart said band between said edges and obliquely thereto whileincluding with at least one of said longitudinal edges in the directionof movement of the band, an angle ranging between 2 and 45, said bandbeing composed of steel,

copper or nickel and having a thickness of the order of 1mm while beingguided over at least two spaced-apart guide rollers, said seam having alength exceeding the circumference of said guide rollers.

2. The belt defined in claim 1 wherein said seam extends helicallythrough at least one complete turn with a pitch angle of substantially 2to 8.

3. The belt defined in claim 1 wherein said band is composed of aplurality of metal-foil loops joined by such seams in endlessrelationship, further comprising a central longitudinal weld seamsecuring juxtaposed longitudinal edges of said loops together.

4. The belt defined in claim 3 whereinsaid oblique seams are alignedwith one another.

5. The belt defined in claim 3 wherein said oblique seams are offsetfrom one another.

6. The belt defined in claim 3 wherein said oblique seams convergetoward one another in the direction of said longitudinal seam.

1. A belt or the formation of a film strip from a film-forming material,comprising a metal-foil band having complementary edges joined togetherin a butt seam with metal bonding flush with the surfaces of the belt,said band being of generally flat configuration with longitudinal edgeslying in planes perpendicular to the band surface, said seam extendingathwart said band between said edges and obliquely thereto whileincluding with at least one of said longitudinal edges in the directionof movement of the band, an angle ranging between 2* and 45*, said bandbeing composed of steel, copper or nickel and having a thickness of theorder of 1mm while being guided over at least two spaced-apart guiderollers, said seam having a length exceeding the circumference of saidguide rollers.
 2. The belt defined in claim 1 wherein said seam extendshelically through at least one complete turn with a pitch angle ofsubstantially 2* to 8*.
 3. The belt defined in claim 1 wherein said bandis composed of a plurality of metal-foil loops joined by such seams inendless relationship, further comprising a central longitudinal weldseam securing juxtaposed longitudinal edges of said loops together. 4.The belt defined in claim 3 wherein said oblique seams are aligned withone another.
 5. The belt defined in claim 3 wherein said oblique seamsare offset from one another.
 6. The belt defined in claim 3 wherein saidoblique seams converge toward one another in the direction of saidlongitudinal seam.